Officials in Tikrit, near Saddam Hussein's hometown, were having difficulty determining exactly what had happened when an explosion destroyed a minibus at 8.30am (0430 GMT) on Friday.
Police Lieutenant-Colonel Saad Abdul Hamid and police Major Hakim al-Azawi, who works at Tikrit hospital where casualties were taken, both said the bomb was hidden in the police minibus and set off as it drove up to the main checkpoint at the eastern entrance to Tikrit, killing at least seven officers and wounding eight.
But an Iraqi National Guard official in Tikrit, Major Salman Abdul Wahid, said the minibus was destroyed by a car bomber who drove up alongside it.
He said nine police officers were aboard the bus and seven of them were killed and two wounded.
Wahid said six other people were injured: two National Guardsmen and four civilians.
Tikrit is 130km north of Baghdad.
In a separate attack, four elite Interior Ministry commandos were killed in Mosul, 370km north of Baghdad.
Iraqi police found the bodies of 14 men, hands bound and wearing blindfolds, shot dead with a bullet to the head in northeastern Baghdad, an Interior Ministry official said.
"The 14 victims were wearing white dishdashas (traditional Arab gowns) and were unearthed. They all had their hands tied and had been shot in the head," an official said.
Locals alerted the police to the fact people were using a bulldozer to bury bodies in a vacant lot in the Kisra wa Atash district.
"When the police arrived on the scene, the driver of the bulldozer ran away. We found two bodies on the spot and 12 more when we dug up the area," the official said.
"The bodies are probably a day or two old, and we think the unidentified victims come from a rural area," he added.
The Interior Ministry official said the neighbourhood is on the edge of Sadr City.